1. Field of the Invention
The present disclosure relates to touch panels, and more particularly to an in-cell type touch panel in which an electrode structure is modified to make a difference of capacitance larger between before and after a touch a capacitive type touch panel for enhancing touch sensitivity.
2. Discussion of the Related Art
As specific examples of the flat display devices, there are a liquid crystal display device LCD, a plasma display panel device PDP, a field emission display device FED, and an electro luminescence display device ELD each of which essentially has a flat display panel in common for producing a picture. The flat display panel is provided with one pair of transparent insulating substrates bonded opposite to each other with a unique light emitting or polarizing material layer disposed therebetween.
Of the flat display devices, the liquid crystal display device displays a picture by controlling light transmissivity of liquid crystals by using an electric field. To do this, the liquid crystal display device is provided with a display panel having liquid crystal cells, a backlight unit for directing the light to the display panel, and a driving circuit for driving the liquid crystal cells.
Recently, requirements for addition of a touch panel to the liquid crystal display device are increasing for perception of a portion of the touch panel touched with a hand or additional input means and transmission of additional information matched to the touch.
And, depending on touch sensing types, in the touch panels, there are a resistance type, a capacitive type, and an infrared ray sensing type, and, recently, the capacitive type is paid attention in small sized models, taking convenience of fabrication, sensing capability, and so on into account.
A related art capacitive type touch panel will be described with reference to attached drawings.
FIGS. 1A and 1B illustrate sections showing states of an electric field before and after a touch a related art capacitive type touch panel respectively, and FIGS. 2A and 2B illustrate equivalent circuits of FIGS. 1A and 1B, respectively.
Referring to FIGS. 1A and 2A, the related art capacitive type touch panel, which employs an interactive capacitive type, is provided with a plurality of driving electrodes 13 Tx formed in directions different from one another on a substrate 10, a plurality of sensing electrodes 11 Rx, and an insulating film 12 formed between layers of the sensing electrodes 11 and the driving electrodes 13.
In this instance, the driving electrodes 13 and the sensing electrodes 11 are arranged adjacent to each other on the same plane. According to this, upon application of a voltage to the driving electrodes 13 Tx: Txn, Txn+1 in succession, a fringe field is formed between the sensing electrode 11 Rx and an adjacent driving electrode 13 to cause capacitance C0.
Referring to FIGS. 1B and 2B, when touched with a touch object, such as a finger or a pen, the touch object functions as a ground source, to form capacitance Cf with the sensing electrode 11 and to change the fringe field formed between the sensing electrode 11 and the driving electrode 13, changing the capacitance to C0′.
According to this, if the driving voltage is applied to the driving electrodes 13 in succession at the time of the touch, a sensing signal is forwarded to the sensing electrode 11 in proportion to an amount of capacitance change C0-C0′ and the driving voltage at the time of the touch.
In this case, though it is required to make the capacitance change C0-C0′ at the time of the touch for making the signal forwarded thus, the related art capacitive type touch panel shown in the drawings, using the fringe field between the sensing electrode and the driving electrode, has small capacitance due to small influence of the fringe field to the interactive capacitance between the driving electrodes and the sensing electrodes, to cause a problem of poor touch sensitivity.
Moreover, if the touch sensitivity is poor thus, a large sized touch panel has poor reliability of touch sensing due to the small amount of change of the interactive capacitance at the time of the touch in comparison to a load which becomes the larger as a distance to an electrode to which the driving voltage is applied the farther.
Thus, the related art capacitive type touch panel has the following problems.
The capacitive type touch panel used currently uses the interactive capacitive sensing type for perceiving multiple touches.
In this case, upon application of the driving voltage to the driving electrode Tx, a sensing voltage at the time of the touch is forwarded to the sensing electrode Rx. At the time of the touch, capacitance between the hand and the electrodes is formed, and the initial capacitance C0 between the driving electrode and the sensing electrode is changed to sensed capacitance C0′ by the change of the fringe field. Therefore, if the driving signal is applied to the driving electrode at the time of the touch, the sensing signal is forwarded to the sensing electrode in proportion to the amount of change of the capacitance and the driving voltage at the time of the touch. Most of the touch electrodes used currently, using the fringe filed, has small capacitance due to small influence of the fringe field to the interactive capacitance between the driving electrodes and the sensing electrodes, to cause a problem of poor touch sensitivity.
Moreover, if the touch sensitivity is poor thus, a large sized touch panel has poor reliability of touch sensing, making application of the related art capacitive type touch panel difficult.